diff --git a/apps/report-execution/pytest.toml b/apps/report-execution/pytest.toml
index 031d3e55ac..932f56312a 100644
--- a/apps/report-execution/pytest.toml
+++ b/apps/report-execution/pytest.toml
@@ -1,6 +1,7 @@
 [pytest]
 pythonpath = ["."]
 testpaths = ["tests"]
+norecursedirs = ["assets"]
 python_files = ["*.py"]
 python_classes = ["Test*"]
 python_functions = ["test_*"]
@@ -10,4 +11,4 @@ addopts = [
     "--strict-config",
     "--showlocals",
     "--import-mode=importlib"
-]
\ No newline at end of file
+]
diff --git a/apps/report-execution/src/execute_report.py b/apps/report-execution/src/execute_report.py
index 1dc7c732d7..59ab99a88f 100644
--- a/apps/report-execution/src/execute_report.py
+++ b/apps/report-execution/src/execute_report.py
@@ -62,7 +62,7 @@ def get_library(library_name: str, is_builtin: bool):
         if is_builtin:
             return import_module(f'src.libraries.{library_name}')
         else:
-            raise errors.ToDoError('support custom libraries')
+            return import_module(f'src.libraries.custom.{library_name}')
     except ModuleNotFoundError:
         # Initial error not helpful for debugging
         raise errors.MissingLibraryError(library_name, is_builtin) from None
diff --git a/apps/report-execution/src/libraries/custom/__init__.py b/apps/report-execution/src/libraries/custom/__init__.py
new file mode 100644
index 0000000000..6d8099d70f
--- /dev/null
+++ b/apps/report-execution/src/libraries/custom/__init__.py
@@ -0,0 +1,2 @@
+# This module contains libraries that deployments mount into this location, but will be
+# empty in the base product
diff --git a/apps/report-execution/tests/integration/assets/custom_library.py b/apps/report-execution/tests/integration/assets/custom_library.py
new file mode 100644
index 0000000000..5626147f13
--- /dev/null
+++ b/apps/report-execution/tests/integration/assets/custom_library.py
@@ -0,0 +1,17 @@
+from src.db_transaction import Transaction
+from src.models import ReportResult, TimeRange
+
+
+def execute(
+    trx: Transaction,
+    subset_query: str,
+    data_source_name: str,
+    time_range: TimeRange | None = None,
+    **kwargs,
+):
+    """This is a stub custom library just to start to get the interface hooked up."""
+    content = trx.execute(subset_query)
+
+    return ReportResult(
+        content_type='table', content=content, description='Custom pass through query'
+    )
diff --git a/apps/report-execution/tests/integration/docker-compose.yml b/apps/report-execution/tests/integration/docker-compose.yml
index 7c9dd6dd04..a0faca53dc 100644
--- a/apps/report-execution/tests/integration/docker-compose.yml
+++ b/apps/report-execution/tests/integration/docker-compose.yml
@@ -3,3 +3,9 @@ services:
   report-execution:
     # allows using localhost db conn for easy access to db container directly or via report-execution container
     network_mode: host
+    # Tests external client library mounting into container works
+    volumes:
+      - type: bind
+        source: ../apps/report-execution/tests/integration/assets/custom_library.py
+        target: /usr/report-execution/src/libraries/custom/custom_library.py
+        read_only: true
diff --git a/apps/report-execution/tests/integration/libraries/custom_library.py b/apps/report-execution/tests/integration/libraries/custom_library.py
new file mode 100644
index 0000000000..8e4a295fba
--- /dev/null
+++ b/apps/report-execution/tests/integration/libraries/custom_library.py
@@ -0,0 +1,35 @@
+import http.client
+import json
+
+import pytest
+
+
+@pytest.mark.usefixtures('setup_containers')
+@pytest.mark.integration
+class TestCustomLibrary:
+    """Integration tests for custom library execution."""
+
+    def test_custom_library_runs(self):
+        report_spec = {
+            'version': 1,
+            'is_export': True,
+            'is_builtin': False,
+            'report_title': 'Test Report',
+            'library_name': 'custom_library',
+            # Filter code is used here as it is a stable, small table
+            'data_source_name': '[NBS_ODSE].[dbo].[Filter_code]',
+            'subset_query': 'SELECT * FROM [NBS_ODSE].[dbo].[Filter_code]',
+        }
+
+        connection = http.client.HTTPConnection('localhost:8001')
+
+        headers = {'Content-type': 'application/json'}
+        body = json.dumps(report_spec)
+
+        connection.request('POST', '/report/execute', body, headers)
+
+        response = connection.getresponse()
+        assert response.status == 200
+
+        result = json.loads(response.read())
+        assert result['description'] == 'Custom pass through query'
diff --git a/apps/report-execution/tests/integration/main.py b/apps/report-execution/tests/integration/main.py
index f5bb6beadd..22338e181f 100644
--- a/apps/report-execution/tests/integration/main.py
+++ b/apps/report-execution/tests/integration/main.py
@@ -36,6 +36,6 @@ def test_report_runs(self):
 
         result = json.loads(response.read())
         assert (
-            result['description']
+            result['header']
             == 'Custom Report For Table: [NBS_ODSE].[dbo].[Filter_code]'
         )